J. Biol. Chem., Vol. 265, Issue 17, 9587-9590, 06, 1990
Human platelets and megakaryocytes contain alternately spliced glycoprotein IIb mRNAs
PF Bray, CS Leung and MA Shuman
Cancer Research Institute, University of California, San Francisco 94143.
The earliest marker of the megakaryocyte lineage in human bone marrow is a
heterodimeric complex of glycoproteins IIb (GPIIb) and IIIa (GPIIIa).
GPIIb-IIIa is a member of the integrin family and serves as a receptor for
fibrinogen and other adhesive glycoproteins on the surface of activated
blood platelets. Mature platelet GPIIb is processed from a single precursor
peptide into a disulfide-linked GPIIb alpha and GPIIb beta chain. To study
possible mechanisms which could determine ligand specificity of the
GPIIb-IIIa complex we investigated whether there are multiple forms of
GPIIb mRNA by screening an unamplified lambda gt10 human erythroleukemia
cell cDNA library. Four GPIIb clones were isolated and sequenced. Two
contained a 102-nucleotide in-frame deletion corresponding to 34 amino
acids in the extracellular domain of GPIIb beta. Polymerase chain reaction
amplification of human erythroleukemia cell cDNA confirmed the presence of
two different transcripts. Normal genomic DNA sequence was shown to contain
consensus splice-donor and splice-acceptor sites indicating a 102-base pair
exon that is spliced in or out. Using primers specific for either
transcript, both forms of GPIIb mRNA were identified by the polymerase
chain reaction in normal human platelets and megakaryocytes, but not in
reticulocytes or two white blood cell lines. These data provide evidence
for two forms of GPIIb in platelets and megakaryocytes and suggest a
mechanism for variations in receptor ligand affinity or localization.